Abstract: An air conditioning system has an evaporative cooler and a refrigerated cooler connected to a common duct connecting both of the coolers to a cooled space. A space thermostat senses space temperature of the cooled space and initiates cooling responsive thereto. A cooler selection control selects one of the coolers for cooling the cooled space responsive to the relative humidity and temperature of air outside the cooled space. The selection control delays starting of the refrigerated cooler a cool down period after the initiation of cooling. With the evaporative cooler employed in a system with, or in a system without, the refrigerated cooler, the evaporative fan is started a wetting period after the starting of the evaporative pump of the evaporative cooler to wet the evaporative pads. Additionally an exhaust vent opens when the evaporative fan of the evaporative cooler is operating and closes when the evaporative fan is stopped.